In torque applying tools such as nutrunners and torque wrenches it is desirable to incorporate a display or printout indicating the torque applied by the tool during use of the tool to tighten threaded fasteners. In assembly line production a tool may be set to tighten bolts to a predetermined torque setting, for example. It is desirable to have a visual display or print-out of the torque actually applied, for quality control and safety purposes. For that reason, torque wrenches and nutrunners often have associated displays of sensed applied torque.
Often however the sensed torque is little more than approximation or estimate of the torque actually applied to the bolt or other threaded fastener. It has never been possible to sense the torque at the drive head itself of the tool due to space limitations at the drive head. The torque sensors or strain gauges necessary to measure the applied torque have typically been spaced along the side handle of a torque wrench or along the drive train between a motor and a bevel drive gear of a nutrunner. It has generally been accepted that errors between the torque as measured at a point somewhat distant from the drive head and the torque exerted by the drive head are small in comparison with the torques being imposed; and are inevitable and unavoidable. The errors may arise, for example, from friction between the meshing teeth of the bevel gears of a nutrunner, or may take the form of cyclical errors arising from inaccuracies In the grinding of those teeth or in the bearings for the drive head. Nevertheless those errors do exist and limit the accuracy of torque sensing in known tools.